An electric generator is a device that is constructed to transform mechanical energy into electrical energy. Accordingly, a generator performs the opposite energy transformations as does an electrical motor (i.e., electrical to mechanical energy transformations). In some cases the same device can act, under different operating conditions, as either a generator or as an electric motor.

The most common generator design is based upon the principles of electromagnetic induction, a process by which a voltage (electromagnetic force or emf) is generated or induced in a circuit by changing magnetic flux. The quantitative relationship between the generated or induced voltage and the magnetic flux is described by Faraday's Law.

In the early part of the nineteenth century Danish scientist Hans Christian Oersted demonstrated a relationship between electricity and magnetism by placing a wire near a magnetic compass. When Oersted applied an electric current to the wire, the magnetic...